I am trying to find a way to make a HashMap return a default value. For example if you look at the following this will printout "Test:=null" what if I want to request a default value so anytime I try to get something that is NOT set in the hashMap I will get the value?
Map<String, String> test = new HashMap<String, String>();
test.put("today","monday");
System.out.println("Test =:" + test.get("hello") + "");
Try the following:
Map<String,String> map = new HashMap<String,String>(){
@Override
public String get(Object key) {
if(! containsKey(key))
return "DEFAULT";
return super.get(key);
}
};
System.out.println(map.get("someKey"));
Better check the return value instead of changing the way a Map works IMO. The Commons Lang StringUtils.defaultString(String) method should do the trick:
Map<String, String> test = new HashMap<>();
assertEquals("", StringUtils.defaultString(test.get("hello")));
assertEquals("DEFAULT", StringUtils.defaultString(test.get("hello"), "DEFAULT"));
StringUtils JavaDoc is here.
Rather than try to give a value to the data, why don't you just do a check when you want to pull the data?
if (!set.containsKey(key)){
return default_value;
}
else{
return set.get(key);
}
No, you can't use it as a switch condition. You can override the get method by extending it into another class or you may try it as follows :
Map<String, String> test = new HashMap<String, String>();
test.put("today", "monday");
String s = test.get("hello") == null? "default value" : test.get("hello");
System.out.println("Test =:" + s);
or
final String defaultValue = "default value";
Map<String, String> test = new HashMap<String, String>() {
@Override
public String get(Object key) {
String value = super.get(key);
if (value == null) {
return defaultValue;
}
return value;
};
};
test.put("today", "monday");
System.out.println("Test =:" + test.get("nokey"));
And also you can achieve this by simply using Properties class instead of HashMap.
Properties properties = new Properties();
properties.setProperty("key1", "value of key1");
String property1 = properties.getProperty("key1", "default value");
String property2 = properties.getProperty("key2", "default value");
System.out.println(property1);
System.out.println(property2);
which prints :
value of key1
default value
Extend the HashMap and override the get().
Map. Note this will break the contract.